Hi,
I've been with a m51 for a month.
I'm happy with the sound: open, spacious soundstage, detailed but smooth sound, the timbre is neutral, voice is natural (a little thin), bass is not realy deep but fast and detailed.
However, I found a problem of the preamp, at the volome > 3db the sound become noisy with pops and cracks,.. noticablly. Even the input was either usb or hdmi or coaxial (from a oppo 95 or mac mini+ AP2) it happened. At volume <=0db, the sound is still clean with black dead background.
Then I talked to a dealer of Nad, they explained it a common issue of M51 (they tested many).
But I don't agree so.
Anyone here ever try the preamp loud enough (volume>3db) to test the issue?
Other than this issue, I'm totally satisfied with the sound quality.
Mine is the latest firmware 1.41.